Due to the characteristics such as energy conservation, environmental protection and easy operation of the membrane isolation technique, the industry of membrane isolation has developed rapidly, and the application scope thereof has been extended to the fields such as biology, medicament, environmental protection, energy sources, municipal water treatment, and waste water treatment. A hollow filtration membrane, due to its large filtration area per unit volume, low cost of the manufacture of equipment, and the realization of cross flow filtration, makes the life time of the filter element greatly extended. However, the current commercialized hollow filtration membrane products generally utilize materials such as polysulfones (PS), polyvinylidene fluorides (PVDF), polyethersulfones (PES), and polyacrylonitriles (PAN), which cannot be widely used due to their low ratios of quality to price.
Polyvinyl chlorides are attracting more and more attention from research units, as they have good physical properties and chemical stability, are resistant to microorganism erosion, acids and bases, and have a lot of sources and varieties, the price of which is low. However, since the hydrophilicity of polyvinyl chloride materials themselves is not good, polyvinyl chloride filtration membranes have no good penetration property and are easily polluted, thus causing the filtration property thereof to decline rapidly.
To produce liquid separation membranes of polyvinyl chloride having excellent properties, it is necessary to improve the hydrophilicity thereof after the membrane is formed. To realize it, the following methods may be employed: (1) copolymerization modification, i.e. introducing other chemical substances having hydrophilic groups into vinyl chloride chain segments by copolymerization; (2) plasma surface modification, i.e. treating polyvinyl chloride powders or membranes with plasma to produce hydrophilic groups containing chlorine on the surfaces of polyvinyl chloride powders or membranes; and (3) surface grafting modification (one of filtration membrane chemical modification), i.e. making polyvinyl chloride molecule chain produce free radicals by high energy radiation such as Y-ray and electron beam, then introducing the desired hydrophilic groups into the membrane surface by graft polymerization. All of the above three methods can realize the improvement of the hydrophilicity property of polyvinyl chloride filtration membrane, but their industrialization is not easy, as the cost is high.
The fourth modification method for polyvinyl chloride filtration membrane is called as co-blend modification, i.e. adding a co-blend material, which is compatible with polyvinyl chloride materials and has hydrophilic groups, into a slurry for preparing the membrane. The less the difference of solubility parameters (representing the solubility property of a macromolecule material) between the two materials is, then the better the compatibility of the two materials is, the more stable the slurry for preparing the membrane is, the more uniform the aperture of the formed membrane is, and the less the drawbacks are. Furthermore, the better the hydrophilicity property of the selected co-blend material is, and the higher the ratio thereof in the slurry for preparing the membrane is, then the higher the water flux of the membrane is, and the better the anti-pollution property thereof is. Therefore, the selection of proper co-blend material and the use of the proper molding technique can produce a polyvinyl chloride hollow filtration membrane having good mechanical properties, high water flux and good anti-pollution property, which has a good quality and low cost.